1. Field of the Invention
The present invention relates generally to an ink jet recording method and an ink jet recording apparatus. More particularly, the present invention relates to an ink jet recording method and an ink jet recording apparatus wherein recording is achieved using an ink jet recording head including a plurality of ink ejection ports.
2. Description of the Related Art
With a conventional recording process having a recording head including a plurality of ejection ports employed therefor, each row of plural dots to be formed by main scanning of a recording head (hereinafter referred simply as a line) is generally formed with ink droplets ejected from the same ejection port.
On the other hand, a pattern of each dot forming a line is classified into two types, one of them being such that one dot is formed by one ink droplet corresponding to binary gray level recording and the other one being such that one dot is formed by a plurality of ink droplets corresponding to multi-level recordings.
A so-called multi-droplet process has been known as one of the conventional method for forming a dot with ink droplets ejected from the same ejection port corresponding to the multi gray level recordings. This type of method is intended to express the gray level of a recorded image by forming one dot (pixel) with a plurality of ink droplets shot onto a single location on a recording medium and then changing a dot area or a dot density depending on the number of ink droplets shot onto the recording medium, and has an advantage that the foregoing method makes it possible to perform a recording operation at a high speed for forming an image with high resolution and high gray level compared with various conventional methods, e.g., a tone production method by density of each element, a tone production method by density pattern, a dither method and an ink density variation method by using plural density of ink.
Although the respective dots forming a line are formed corresponding to binary gray level recording or the multi gray level recording, a problem such as running over of ink or bleeding, which is described below, may occur. Especially, the problem such as bleeding may appear when intending to achieve a high quality recorded image by solving the problem described below which may occur in the case that the dots are formed with ink droplets ejected from the same ejection port, so that the high quality recorded image can not be achieved.
With respect to a plurality of ejection ports on the recording head, in the case that the direction of ejection of ink droplets from the ejection ports and a quantity of ink ejected from the same ejection port fluctuate from ejection port to ejection port, there arises an occasion that a certain stripe appears on a recorded image which should originally have constant density variation or a density of the image fluctuates. More specifically, in the case that the direction of ejection of ink droplets fluctuates, the position of a dot formed on a recording paper serving as a recording medium is offset from an original one, resulting in a stripe appearing on the recorded image. When a quantity of ink ejected from the ejection ports fluctuates, a size of each dot formed on the recording paper or a density of the same fluctuates. As a result, there arises an occasion that the density of the recorded image fluctuates.
As a measure to be taken for avoiding the foregoing problems, a proposal has been made with respect to a method of producing a recording head at a very high accuracy in order to suppress fluctuation in the direction of ejection of ink from each ejection port and a quantity of ink ejected from the same as far as possible. However, with the proposed method as mentioned above, there arises a problem that each recorded image is obtained not only at a high production cost but also at a reduced yielding rate.
In addition, as a measure to be taken for obviating a malfunction of fluctuation in density, a proposal has been made with respect to a method of changing the number of shot ink droplets so as to eliminate variation of a quantity of ejected ink among a plurality of ink ejection ports on a recording head. However, in the case that the proposed method is installed in a working system for executing the proposed method, there arises a problem that a running cost of the working system is undesirably increased. Further, it is found that the proposed method is unexpectedly ineffective for preventing a stripe from appearing on a recorded image. In the case that fluctuation in a quantity of ejected ink among the ejection ports varies as time elapses, it becomes necessary to adjust the number of shot ink droplets again. This leads to a problem that each maintenance service for the working system is unsatisfactorily achieved.
To solve the aforementioned problems, an improved recording method is disclosed in an official gazette of, e.g., Japanese Patent Application Laying-open No. 107975/1985. According to this prior art, to reduce variation of the direction of ink ejection and a quantity of ejected ink among a plurality of ejection ports, and moreover, hardly visualize stripe and fluctuation in density, a single line extending in the main scanning direction is formed by a plurality of ink droplets ejected from the ejection ports.
FIG. 1 is a schematic view which illustratively explains the recording method to be practiced according to the prior art. Specifically, pixels not located adjacent to each other not only in the vertical direction but also in the transverse direction are recorded on a recording paper (not shown) by preceding main scanning (hereinafter referred to as preceding scanning) with a recording head, and subsequently, the recording paper is fed in the auxiliary scanning direction by a distance equal to a half of the length of a row of ejection ports so that the remaining pixels failing to be recorded by the preceding scanning are recorded on the recording paper by subsequent scanning. According to the above-described prior art, for example, in the case that all pixels located on each line as illustrated by xe2x80x9cimage dataxe2x80x9d in FIG. 1 are formed on the recording paper, a row of dots arranged in the main scanning direction (i.e., a line) is formed with ink droplets ejected from two different ejection ports. Thus, distribution of the dots in the ink ejecting direction is averaged, resulting in stripe on the line being hardly visualized. With the recording method shown in FIG. 1, when it is assumed that variation of a quantity of ink ejection among the ejection ports is normally distributed with a standard deviation "sgr", the variation of a quantity of ink ejection among a plurality of lines is reduced to a level of "sgr"/{square root over (2)}. Consequently, since variation of a quantity of ejected ink among the lines is visually recognized as variation of density among the lines, the recorded image having few fluctuation in density is obtainable.
For example, as illustrated by xe2x80x9cimage dataxe2x80x9d in FIG. 2, in the case that a specific halftone image (i.e., all pixels are not formed) is recorded on a recording paper (not shown), since a row of dots arranged in the main scanning direction is formed by ink droplets ejected from the same ejection port when the foregoing conventional recording method is employed, there arises a problem that fluctuation in stripe and density can not be reduced at all.
Another recording method of hardly visually recognizing stripe and fluctuation in density is disclosed in U.S. Ser. No. 894,555 which was proposed by common assignee to the present invention. According to this prior art, in association with assignment of image data to ejection ports, ink dots forming a row of dots arranged in the main scanning direction (i.e., a line) are sequentially assigned to scannings different from each other. Once this conventional recording method is employed, not only in the case that all pixels as illustrated by xe2x80x9cimage dataxe2x80x9d in FIG. 1 are formed but also in the case that a halftone image as illustrated by xe2x80x9cimage dataxe2x80x9d in FIG. 3 is recorded on the recording paper, since each line is formed by ink droplets ejected from two different ejection ports as illustrated by xe2x80x9crecording methodxe2x80x9d in FIG. 3, stripe and fluctuation in density can be reduced without fail.
With this conventional recording method, however, depending on the type of image data, there arises an occasion that a group of continuous adjacent dots is formed by the same scanning as illustrated by xe2x80x9crecording methodxe2x80x9d in FIG. 4 to form a row of dots arranged in the auxiliary direction. When a row of dots arranged in that way appears in the course of a recording operation on the recording paper having poor ink absorption, ink droplets for forming a group of adjacent dots on the recording paper are united with each other and run over before they penetrate into the recording paper, resulting in a recorded image being visually recognized with an irregularly deformed pattern. In such case, there arise problems that especially, the shape of each edge portion of the recorded image can not clearly be recognized, and in the case of color recording, two inks each having a different color are mixed with each other, resulting in the recorded color image failing to be clearly recognized (the foregoing problems are hereinafter referred to as bleeding).
The conventional recording methods disclosed in Japanese patent Application Laying-open No. 107975/1985 and U.S. Ser. No. 894,555 are employable for either of binary gray level recording and multi gray level recording with appearance of the foregoing problems in association with the formation of each recorded image on the recording paper.
In the case of multi gray level recording for forming a single dot with a plurality of ink droplets, several unique recording methods each available for solving the problems attributable to variation of a quantity of ejected ink among a plurality of ejection ports have been known, and each of the recording methods has similar problems to be improbably solved. These recording method and the problems to be solved with the latter will be described later.
A multi gray level recording method of reducing a malfunction attributable to stripe or the like associated with variation of a quantity of ejected ink among a plurality of ejection ports is exemplified by the method disclosed in U.S. Ser. No. 893,086. FIG. 5 is a schematic view which illustratively explain the conventional multi gray level recording method.
More specifically, an image is recorded by plural times of scannings by forming a same line with ink droplets ejected from different ejection ports. According to this prior art, for example, in the case that a pixel as illustrated by xe2x80x9cimage dataxe2x80x9d in FIG. 5 (i.e., a pixel formed by three ink droplets), since the pixel is formed with ink droplets ejected from three different ejection ports, distribution of pixels in the ink ejection direction is averaged, resulting in stripe on a recording paper (not shown) being hardly recognized. When it is assumed that variation of a quantity of ejected ink among a plurality of ejection ports is normally distributed with a standard deviation of "sgr", variation of a quantity of ejected ink among a plurality of lines is reduced to a level of "sgr"/{square root over (3)}. Since the variation of a quantity of ejected ink among the lines is visually recognized as variation of a density of ejected ink, a recorded image having few fluctuation in density can be obtained with the multi-level recording method.
Also, the multi gray level recording method has problems as noted below. More specifically, in the case that xe2x80x9cOxe2x80x9d pixels as illustrated by xe2x80x9cimage dataxe2x80x9d in FIG. 5 are recorded on a recording paper, i.e., in the case that pixels each formed with a single ink droplet are recorded on the same, since a row of dots arranged in the main scanning direction are formed with ink droplets ejected from same ejection port, there arises a problem that fluctuation in stripe and density can not be reduced at all.
In addition, a multi gray level recording method of hardly recognizing fluctuation in stripe and density is exemplified by the method disclosed by U.S. Ser. No. 894,555.
As shown in FIG. 6, the multi gray level recording method is practiced by sequentially assigning the formation of dots within the range defined by a single line extending in the main scanning direction to scannings different from each other. With this conventional recording method, not only in the case that all pixels are recorded on a recording paper (not shown) but also in the case that a halftone image is recorded on the same, a single line extending in the main scanning direction is formed with ink droplets ejected from a plurality of different ejection ports in the same manner as that shown in FIG. 3. Thus, stripe and fluctuation in density can be reduced without fail.
With this conventional recording method, however, since a group of continuous adjacent dots for forming a row of dots arranged in the auxiliary scanning direction are recorded by same scanning, there arises an occasion that a malfunction of bleeding as mentioned above occurs. This is an especially significant problem in the case of multi gray level recording for forming a single dot (i.e., a single pixel) with a plurality of ink droplets.
An object of the present invention is to provide an ink jet recording method and an ink jet recording apparatus which assure that a high quality image can be recorded while attenuating the problem of running of ink or bleeding.
Another object of the present invention is to provide an ink jet recording method and an ink jet recording apparatus which assure that a high quantity image can be recorded while resolving the above-described problem regarding the ink or the like as well as attenuating the problem attributable to fluctuation in a quantity of ink ejected from each ejection port in the case that recording is effected by employing a two-level recording process or a multi-level recording process.
A further object of the present invention is to provide an ink jet recording method and an ink jet recording apparatus which resolve the above-described problem regarding the running over of ink or the like, and which assure that a high quantity image can be recorded not only with few stripe and few fluctuation in density but also with excellent image sharpness at edge portions of the image wherein the number of ejection ports each capable of recording a row of dots in the main scanning direction is set to be plural, and moreover, dots continuously located adjacent to each other in the auxiliary scanning direction are formed with scannings possibly different from each other.
In a first aspect of the present invention, an ink jet recording method of performing a recording operation with dots each formed on a recording medium with ink ejected from a recording head including a plurality of ejection ports, the method comprises the steps of;
executing assignment based on image data to one of the ejection ports to build a plurality of lines with the dots and to which-numbered scanning to be achieved for ink ejection when the recording operation is performed so as to build the plural lines with the dots formed by plural times of scanning achieved by the recording head,
wherein the order of the ejection ports and the scannings are assigned in such a manner that a plurality of dots for building the plural lines are formed by ejecting the ink from the ejection ports different from each other in accordance with an order of plural times of scannings different from each other, and
the order of the scannings to be effected for ink ejection for building the lines with the dots is assigned on the basis of an order of scannings for the dots to which assignment has been already executed, on a specific line having the dots belonging thereto while the dots are arranged for building the lines, and on a row of dots located in the direction of extension of the lines,
performing the plural times of scannings with the recording head, and
forming the dots to which the order of scanning is assigned by ejecting the ink from the ejection ports assigned on completion of each of the plural times of scannings.
In a second aspect of the resent invention, an ink jet recording method of building a recorded image by ejecting ink from a recording head toward a recording medium to form a plurality of dots arranged in a matrix-shaped pattern, the method comprises the step of;
building the recorded image within a whole density range, wherein in the case that two dots located adjacent to each other in a row of dots extending in a first direction of the matrix-shaped pattern or in a second direction different from the first direction, are formed the two dots being formed with a time difference equal to or more than a predetermined time therebetween and in the case that a set of the two dots is randomly located.
In a third aspect of the present invention, an ink jet recording apparatus for performing a recording operation with dots each formed on a recording medium with ink ejected from a recording head including a plurality of ejection ports, the apparatus comprises;
assigning means for executing assignment based on image data to one of the ejection ports to build a plurality of lines with the dots and to which numbered scanning to be achieved for ink ejection when the recording operation is performed so as to build the plural lines with the dots formed by plural times of scannings achieved by the recording head,
wherein, the assigning means serving to execute assignment to an order of the ejection ports and the scannings in such a manner that a plurality of dots for building the plural lines are formed by ejecting the ink from the ejection ports different from each other in accordance with an order of plural scannings different from each other, and
the order of the scannings to be effected for ink ejection for building the plural lines with the dots is assigned on the basis of an order of scanning for the dots to which assignment has been already achieved, on a specific line having the dots belonging thereto while the dots are arranged for building the plural lines, and on a row of dots located in the direction of extension of the lines;
scanning means for performing the plural times of scannings with the recording head; and
recording/controlling means for forming the dots to which the order of scannings is assigned by ejecting the ink from the ejection ports assigned on completion of each of the plural times of scannings.
In a fourth aspect of the present invention, an ink jet recording apparatus for performing a recording operation with dots each formed on a recording medium with ink ejected from a recording head including a plurality of ejection ports, the apparatus comprises;
assigning means for executing assignment based on image data to one of the ejection ports to build a plurality of lines with the dots and which-numbered scanning to be achieved for ink ejection when the recording operation is performed so as to build the lines with the dots formed by plural times of scannings achieved by the recording head,
wherein, the assigning means serving to execute assignment to an order of the ejection ports and the scanning in such a manner that a plurality of dots for building the plural lines by injecting the ink from the ejection ports in accordance with the order of plural scannings different from each other, and
the order of the scannings to be effected for ink ejection for building the plural lines with the dots is assigned on the basis of an order of scanning for the dots to which assignment has been already achieved, on a specific line having the dots belonging thereto while the dots are arranged for building the line, and on a row of dots located in the direction of extension of the plural lines;
scanning means for performing scanning with the recording head;
paper feed means for feeding the recording medium every time the scanning is performed; and
recording/controlling means for forming dots to which the order of scannings is assigned by ejecting the ink from ejection ports assigned on completion of the scanning, the ejection ports assuming the positions corresponding to the conveyance of the recording medium.
In a fifth aspect of the present invention, an ink jet recording method of performing a recording operation with dots each formed on a recording medium with ink ejected from a recording head including a plurality of ejection ports while scanning of the recording head is executed;
wherein when the scanning is assigned to the dot for forming the dot, the assignment is executed considering a two dimensional arrangement of the dots including the dot.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.